The present invention relates to a speed governor for a music box.
In a music box driven by a main spring, for example, a speed governor or regulator is provided to control play at a constant speed.
An air governor system used for controlling the play speed by using the air resistance of a fan running at a high speed, and a centrifugal governor system which controls the speed by using weights which move radially due to centrifugal force and a brake part with which an outer periphery of the weight contact have been generally known hitherto.
Both of the above systems are effective to rotate a worm shaft with a worm gear driven by the gear train to be regulated, and the fan or the weights are mounted on the worm shaft.
Although the above air governor system is simple in construction, it is disadvantageous in that the force controlling the speed is small. Namely, it is difficult to always keep the gear train at a constant speed in such a governor system since the air resistance of the fan is utilized merely upon a change in the driving forces applied to the gear train to be regulated. When a spring serves as a driving source the driving force is varied from the initial stage when the wound-up spring begins to be released, to subsequent stages. In order to obtain a large controlling force in this system, it is necessary that the air resistance be increased by enlarging the size, particularly, the diameter of the fan or otherwise by increasing the speed acceleration ratio with respect to the driving source. However, a spacing problem would be caused by enlarging the fan. Also, the number of teeth of the gear constituting the wheel train will have to be adjusted to increase the speed acceleration ratio. Another problem in mechanical strength will arise in minimizing a pitch of the gear, and hence the pitch cannot be so minimized below a certain limit.
The centrifugal governor system is advantageous in that it provides a large force for controlling the speed, i.e. brake power, as compared with the air governor system; however, the brake part must be provided around the weight part, which is not preferable. Further, another disadvantage arises such that a stop member for the music box will be limited as to location.
With reference to the stop member for the music box, a problem is also unavoidable in the air governor system. The fan consists of a thin metal strip or blade which functions to stop the operation of the music box, in other words, to stop the gear train in cooperation with the stop member. In this case, however, an overload which may damage the worm shaft and its bearing could be imposed thereon. Therefore, these members must be provided with suitable strength and construction. The fan is mounted on the worm shaft through a press fit, which may damage the worm, and hence the worm shaft must be subjected to quench hardening beforehand.